Maclean Watt was born at Grantown-on-Spey, Morayshire, although his mother was a native of Skye, and he was educated at Edinburgh University (MA, BD). Licensed by the Presbytery of Dalkeith on 12 May 1896, he was minister of Turriff (1897–1901), of Alloa and Tullibody (1901–11), of St. Stephen’s, Edinburgh (1911–23), and of the High Kirk known as Glasgow Cathedral (1923–34). In 1907 he accompanied the King of Denmark to Iceland as a correspondent for The Times, The Scotsman and The Manchester Guardian. During the War he was a chaplain with the Gordon Highlanders in the 7th Division, and he was sent by the Government as Commissioner to the US and Canada in 1918. He was a prolific author in prose and verse, on folk-lore, history and antiquities, especially Celtic and Gaelic as well as aspects of religion, literature and the life of a soldier, and gave the Warrack Lectures and McNeil-Frazer Lectures on preaching in 1930. He was Turnbull Trust preacher at The Scots' Church in Melbourne in 1932.